DISEASES OF PLANTS. 761 



capable of producing scab on potatoes was shown, and soaking the 

 seed tubers in corrosive sublimate solutions for l.i hours before plant- 

 ing gave good results in preventing scab and also the disease due to 

 Rhizoctonia solani. 



Notes are given of the occurrence of club root of crucifers, Penicil- 

 Hum glaucum on asparagus, mildew of spinach (Peronospora efusa), the 

 mildew of cucurbits (Splicer otheca castagnei), smuts of cereals, and vari- 

 ous diseases of fruit trees. 



The more destructive insects of these different plants are enumerated, 

 and a brief account is given of the continued studies on the contents 

 of the stomachs of the rook (Gorvus frugilegus). Definite conclusions 

 relative to the nature of the rook, whether injurious or beneficial to 

 the farmer, are not yet given, and the investigations are to be continued. 



Concerning attacks of black rot, A. Prunbt (Gompt. Rend. Acad. 

 Sci. Paris, 125 [1897), No. 15, pp. 0.50-553).— The author was appointed 

 by the Minister of Agriculture of France to make a study of the black 

 rot of grapes. He has established the periodicity of the disease as 

 shown by tbe appearance of tho well-known spots on the leaves, sev- 

 eral attacks occurring during a season. Similar observations are 

 reported by several other investigators. 



The severity of the attack is estimated from the abundance of spots 

 on the leaves, and in general the disease seemed to increase rapidly in 

 severity from the first to the third attack, after which it decreased 

 slowly until about the fifth appearance, when it disappeared quite rap- 

 idly. The maximum attack on the leaves is about simultaneous with 

 the first invasion of the fruit. 



Taking into account the climate, atmospheric conditions, etc., it may 

 be stated that the most disastrous attack on the leaves and axillary 

 organs takes place about flowering time and on the fruit it takes place 

 about the time the grapes are the size of small peas. These two 

 periods usually occur the first in June and the second in July, and are 

 preceded by two invasions of increasing severity. The duration of an 

 invasion for the period of susceptibility to attack varies from 5 to 8 

 days, dependent on atmospheric conditions, especially the temperature. 



In a subsequent publication J. Perraud ] gives his observations made 

 in L896 and 1897 in the southeast of France. In general his conclu- 

 sions relating to the periodicity of development of the black rot agree 

 with the above. 



Observations on canker in plum trees, Duke of Bedford and 

 S. U. Pickering (Rpt. Woburn Expt, Fruit Farm , 1897 ', pp. 104-1 '07).— 

 Notes are given on an apparently hitherto unrecorded disease of plum 

 trees which was due to Nectria ditissima. The disease was first noted 

 in the autumn of 1895, when it was found that in a few cases the cortex 

 of a large portion of the stem and of some of the main branches was 

 entirely dead and rotten. The disease had penetrated to a considerable 



1 Compt. Rend. Acad. Sci. Paris, 125 (1897), No. 19, pp. 728-730. 



